Selecting a Solar Pool Heater

A solar pool heating system usually costs between $3,000 and $4,000 to buy and install. This provides a payback of between 1.5 and 7 years, depending on your local fuel costs. They also typically last longer than gas and heat pump pool heaters. Your actual cost and payback depend on many factors. Therefore, before you purchase and install a solar pool heating system, you should do the following:

Evaluating Your Site's Solar Resource for Solar Pool Heating
Before you buy and install a solar pool heating system, you first need to consider your site's solar resource. The efficiency and design of a solar pool heater depends on how much of the sun's energy reaches your building site.

Solar pool heating systems use both direct and diffuse solar radiation. Therefore, even if you don't live in a climate that's warm and sunny most of the time—like the southwestern United States—your site still might have an adequate solar resource. Basically, if your building site has unshaded areas and generally faces south, it's a good candidate for a solar pool heating system.

Your local solar system supplier or installer can perform a solar site analysis. If you'd like to try to do it yourself, see the Evaluation Tools under Learn More on the right side of this page (or below if you've printed it out)

Sizing a Solar Swimming Pool Heating System
Solar system contractors use worksheets and computer programs to help determine system requirements and collector sizing.

Basically, the surface area of your solar collector should equal 50%–100% of the surface area of your pool. In cooler and cloudier areas, you may need to increase the ratio between the collector area and the pool surface area. Adding collector square footage also lengthens the swimming season.

For example, a 15-by-30-foot outdoor swimming pool in Florida typically requires a collector that equals 100% of the pool's square footage to accommodate year-round use. This equals 450 square feet of collectors. In northern California, most people use outdoor pools 6–8 months per year, so they typically size their systems at 60%–70% of the pool's surface area.

In any climate, you can usually decrease the required collector area by using a pool cover.

You'll also want a properly sized pool pump for a solar system. If you're replacing a conventional pool heating system with a solar system, you may need a pump larger than your current one or a separate, smaller pump to move the pool's water to and through the collectors.

Determining the Efficiency of Solar Swimming Pool Heating System
You can determine the efficiency of a solar swimming pool heating system based on the collector's thermal performance rating if available.

A solar collector's thermal performance rating is measured by Btu (British thermal unit) per square foot per day:

Btu/(ft2day)

Or, the rating can be measured by megajoules (MJ) per square meter per day:

MJ/(M2day)

It can also be measured by Btu per day, which is simply the rating in Btu/(ft2day) multiplied by the area in ft2. Also used is MJ per day, which is the rating in MJ/(M2day) multiplied by the area in M2.

The higher the number, the greater the solar energy collection efficiency. However, because weather conditions, instrumentation accuracies, and other test condition constraints can vary, the thermal performance of any two collectors should be considered approximately the same if their ratings are within 25 Btu/(ft2day) of each other.

High efficiency solar collectors not only will reduce your annual operating costs, but may also require fewer square feet of collector area to heat the pool.

Don't choose a solar pool heating system based solely on its collector efficiency. When selecting a solar pool heater, it's also important to consider the following:

Size
Costs.

Comparing Solar Swimming Pool Heating System Costs

Solar pool heaters represent one of the most cost-effective uses of solar energy today.
Photo credit: Heliocol.

Before purchasing a solar pool heating system, you can estimate and compare the costs of using different solar collector models. This will help you determine the potential cost savings of investing in a more efficient type of collector, which may require fewer panels for the collector area needed to heat your pool.

To estimate and compare costs, you need to know the following:

A collector's thermal performance rating (Btu/day)
Total number of collector panels or piping for the area needed to heat your pool
Total installed cost of system.
You can then calculate a collector's energy output per dollar spent or invested using this formula:

(Btu/day X # of collector panels/piping modules) ÷ total installed cost of system = Btu/$ per dollar spent

Example:

(27,900 X 4) Btu ÷ $3,000 = 37.20 Btu/day per dollar spent

If you just know the prices and thermal performance ratings (Btu/day) of collectors, you can use the following formula to calculate the energy output for each dollar spent or invested for different collectors:

Btu/day ÷ collector price = Btu/day per dollar spent

Example:

21,000 Btu ÷ $387 = 54.26 Btu/day per dollar spent

Don't choose a solar pool heating system or collector based solely on its estimated costs. When selecting a solar pool heater, it's also important to consider all of the factors involved in the system's sizing and quality of the design and installation.